A variety of two phase α/β-titanium and near α-titanium alloys, such as Ti—6Al—4V, IMI 834 (Ti—5.8—Al—4Sn—3Zr—0.7Nb—0.5Mo—0.35Si—0.06C) and TIMET 1100 (Ti—6Al—2.7Sn—4Zr—0.4Mo—0.45Si) show great potential application in the air plane and space industry.
Among them Ti—6Al—4V exhibits the broadest application due to an optimum combination of high strength and fracture toughness and excellent fatigue properties at room and elevated temperature. These alloys have, however, some disadvantages such as a poor oxidation resistance above 475° C. (α-case formation), insufficient creep strength at 600° C. and higher temperatures and a poor wear resistance at room and elevated temperatures. The α-case causes crevice formation on the oxidised surface and has a detrimental effect on the fatigue properties. The arc melting process of these relatively high melting point alloy of about 1660° C.) and the necessary melt overheating to about 1750 to 1770° C. is a very energy consuming procedure for the manufacture of investment castings for the air plane and automotive industry, and engineering purposes in general.
Low silicon-containing titanium-based alloys are well known. Thus JP 2002060871 A describes a titanium alloy containing 0.2-2.3 wt % Si, 0.1-0.7 wt % O (total content oxygen), and 0.16-1.12 wt % N and 0.001-0.3 wt % B and remainder of titanium including unavoidable impurities, used for as cast products. These are e.g. golf club heads, fishing tackles and medical components such as tooth root, implants, bone plates, joints and crowns. The low silicon-containing titanium-based alloy does, however, suffer from a disadvantage, by forming small needle like Ti3Si precipates along grain boundaries, which decrease the fracture toughness and ductility of this material.
There is thus a need for an alloy that has a high strength at high temperatures, has a lower melting point than the Ti—Al—V alloys and has good casting properties.